Mechanical ventilation with administration of supplemental oxygen remains the mainstay of treatment of infants and children with respiratory failure. Unfortunately, each of these interventions may produce severe lung damage, and their combined effects may induce permanent impairment of lung function. Currently there are efforts in several areas to elucidate the mechanism of lung injury induced by oxygen, and to develop means to detect oxygen toxicity clinically early enough to aid in minimizing or treating the illness. Identification of specific circulating markers of oxygen toxicity might provide the best means to detect early oxygen toxicity. The proposed pilot project will test the hypothesis that exposure of newborns to high concentrations of oxygen will results in detectably increased concentrations of glutathione disulfide and lipid hydroxy acids, indicators of oxidative stress, in arterial blood. Further, a correlation will be sought between degree of elevation of these markers substances and degree of deterioration of lung function. Finally, the hypothesis that increased levels of these substances correlate with the incidence of chronic lung disease in infants will be tested by following the infants for several months after initial study with frequent clinical assessments of pulmonary symptomatology and function.